Adding and removing User control from Placeholder

Question

What I am trying to achieve that if a user control already added to placeholder then it will be removed otherwise will be added to it and it will be done in a LinkButton's onclick.

The code:

public partial class SiteSettings : System.Web.UI.Page {
    private UserSettings UserSettingsControl;
    protected void Page_Load(object sender, EventArgs e) {
        System.Diagnostics.Debug.WriteLine("Pageload");
        UserSettingsControl = LoadControl("~/UserControls/UserSettings.ascx") as UserSettings;
    }

    protected void UserLink_Click(object sender, EventArgs e) {     
        if (SettingsPlaceholder.Controls.Contains(UserSettingsControl)) {
        System.Diagnostics.Debug.WriteLine("Contains");
        SettingsPlaceholder.Controls.Remove(UserSettingsControl);
        } else {
        System.Diagnostics.Debug.WriteLine("Does not Contains");
        SettingsPlaceholder.Controls.Add(UserSettingsControl);
        }
    }
}

Now it is not working. And I am getting:

Pageload // on first time load
Pageload // on first time click
Does not Contains // on first time click
Pageload // on second time click
Does not Contains // on second time click

in the Output window.

How can I achieve this? I also tried to store it into ViewState, but since UserControl is not serializable so that didn't worked.

The aspx page is:

<telerik:RadAjaxManager ID="AjaxManager" runat="server">
    <AjaxSettings>
        <telerik:AjaxSetting AjaxControlID="UserLink">
            <UpdatedControls>
                <telerik:AjaxUpdatedControl ControlID="SettingsPanel" LoadingPanelID="LoadingPanel" UpdatePanelRenderMode="Block" />
                <telerik:AjaxUpdatedControl ControlID="PlaceHolderPanel" />
            </UpdatedControls>
        </telerik:AjaxSetting>            
    </AjaxSettings>
    <ClientEvents OnResponseEnd="respondEnd" />
</telerik:RadAjaxManager>
<asp:Panel ID="SettingsPanel" runat="server">
    <telerik:RadSplitter ID="MainSplitter" runat="server" MinHeight="200" Width="100%"
        OnClientLoaded="splitterLoaded" OnClientResized="splitterLoaded">
        <telerik:RadPane ID="LeftPane" runat="server" MaxWidth="250" Width="150" MinWidth="150" CssClass="left-rounded-corner settings-splitter-left">
            <asp:Panel runat="server">
                <asp:LinkButton ID="UserLink" runat="server" onclick="UserLink_Click" Text="User Settings" />                    
            </asp:Panel>
        </telerik:RadPane>
        <telerik:RadSplitBar ID="Splitbar" runat="server" CollapseMode="Forward" />
        <telerik:RadPane ID="RightPane" runat="server" CssClass="right-rounded-corner settings-splitter-right">
            <asp:Panel ID="PlaceHolderPanel" runat="server" Height="100%">
                <asp:PlaceHolder runat="server" ID="SettingsPlaceholder" />
            </asp:Panel>
        </telerik:RadPane>
    </telerik:RadSplitter>
</asp:Panel>
<telerik:RadAjaxLoadingPanel ID="LoadingPanel" runat="server" />

---

Edit:

Modified code:

public partial class SiteSettings : System.Web.UI.Page {

            protected void Page_Load(object sender, EventArgs e) {
                    if (!IsPostBack) {
                        AddUserSettings();
                    }
            }

            public UserControl UserSettingsControl {
                    get {
                            if (ViewState["UserSettings"] == null) {
                                    ViewState["UserSettings"] = LoadControl("~/UserControls/UserSettings.ascx") as UserSettings;
                            }
                            return (UserControl)ViewState["UserSettings"];
                    }
            }

        public UserControl SpaceSettingsControl {
                get {
                        if (ViewState["SpaceSettings"] == null) {
                                ViewState["SpaceSettings"] = LoadControl("~/UserControls/SpaceSettings.ascx") as SpaceSettings;
                        }
                        return (UserControl)ViewState["SpaceSettings"];
                }
        }

        protected void SettingsLink_OnCommand(object sender, CommandEventArgs commandEventArgs) {
                switch (commandEventArgs.CommandName) {
                    case "User":
                            AddUserSettings();
                            break;

                    case "Space":
                            AddSpaceSettings();
                            break;
                }
        }

        private void AddUserSettings() {
                AddSettings(UserSettingsControl);
        }

        private void AddSpaceSettings() {
                AddSettings(SpaceSettingsControl);
        }

        private void AddSettings(UserControl control) {
                SettingsPlaceholder.Controls.Add(control);
        }
}

Answer 1

Create a Property in your WebForm like below.

public UserSettings UserSettingsControl 
{
    get
    {
        if (Session["MyControl"] == null)
            Session["MyControl"] = 
            LoadControl("~/UserControls/UserSettings.ascx") as UserSettings;
        return (UserSettings)Session["MyControl"];
    }
}

Now you can access the memory of UserSettingsControl. As it will persist across the Postback. In the original code, the UserSettingsControl was being reset to null across PostBack.

---

By end of the Page Life Cycle all the controls created at runtime will be disposed. Finally, you cannot find the control created at runtime after Postback. Only Recreation of the same control will be required on each PostBack.

Answer 2

You could just not use a PlaceHolder and have the control there the whole time. Then the linkButton could toggle the visibility of the control.

The main problem is that the you are adding the control to the page linkButton click. Dynamically added controls work best when added in the Page_Init and Page_PreInit this allows them to maintain their ViewState. Also they have to be added to the placeholder on every postback. If in your example another control causes a postback after the SettingsControl is added to the placeholder, then the SettingsControl will disappear because it is not being added on every postback.